The technology for forming low-loss optical fibers has advanced to a point where there is widespread commercial manufacturing of optical fibers. Most processing includes drawing an optical fiber from a previously manufactured glass boule, sometimes referred to as a fiber preform. Extremely long lengths of fiber can be obtained by splicing a plurality of lengths, which are obtained using current fusion splicer techniques. Additionally, it has become increasingly more common to splice optical fibers, which have broken, either accidentally, or during appropriate proof testing. For these and other applications, splicing in which the coating material is removed from end portions of two fibers, which are then fused together end to end, provides a suitable means for joining the ends of two glass fibers with an acceptably low splice loss.
Fusion splice losses depend mainly on the mismatch of mode-field diameter (MFD) and misalignment of the cladding/core of two fibers due to either the fiber refractive index design or the inappropriate fusion processes being used. With the help of image techniques, information on the MFD mismatch can be obtained and analyzed by monitoring the deformation/misalignment of the cladding/core of the fibers during the fusion process, see e.g. EP 1 014 070. Such a monitoring system includes typically a charged-coupled device (CCD) camera equipped with an image processor. By use of suitable theoretical models and the information obtained from the images, an estimation method for evaluation of splice losses can be established.
The estimation method as a passive technique for evaluation of splice losses is widely used in most automated fusion splicers of today. Different models for evaluation of splice loss have been explored and developed during the past two decades. Well-known methods for splice loss estimation include the butt-joint approximation and the mode coupling theory. More advanced methods, e.g. hot-image techniques for real-time analysis of cladding and core deformation have also been developed.
In order to achieve the best performance and maximize the flexibility of the estimation method, the models used for splice loss estimation include usually a number of free parameters, called estimation parameters. The optimization of these estimation parameters in order to achieve the best performance of the estimation method has nowadays become one of essential features in the development of splicing techniques. In practice, the estimation parameters are manually optimized according to different types of on-test fibers and the fusion processes being used.
Due to primarily technical reasons and rather complicated nature of the involved splicing processes, the optimization of the estimation parameters is a quite difficult and time consuming job that may only be performed by very experienced engineers.
The time typically needed for manually optimizing the estimation parameters on a given fiber combination is as long as a few days which is hardly to be accepted by splicer users, especially, when frequently changes of fusion processes and fiber combinations are involved, e.g. in the manufacture of erbium doped fiber amplifiers (EDFA). This is hardly acceptable for the splicer user, and such optimization has thus typically to be performed by the fiber splicer manufacturer.